(For the record, Krispy Kreme is also great. Dunkin' Donuts is the least exciting of the three but mostly because I'm see/go to it all the time. I'm just a sucker for donuts.)
As a teenager I remember we used to hang out in the local 24hr Tim Hortons waiting for the fresh doughnuts to come out of the oven in the wee hours of the morning, after partying all night. Delicious, but that's gone now. It's silly that most people in Canada still associate Tim Hortons with Canadian culture/cuisine.
The coffee is decent if you're road tripping, and it's eminently cheaper/better than Starjunk. But I always opt for independent coffee and/or doughnut spots whenever possible.
I hope this comment doesn't come across as mean.
I'm an American, who curls and knows a lot of Canadiens and has been to Canada a bunch.
Come on :D